OK, so you want to accept empty strings as well.
The simplest way is to use getline instead of >>
The difference, of course, is that this will read an entire line into a string, not up to first whitespace.
using namespace std;
while (getline(cin, s))
cout << "\"" << s << "\"\n";
Also, if there are lots of cin >> 's in the program, you should empty the input buffer after using >> and before using getline: